A portable electronic device used in mobile phones, personal digital assistances and the like may comprise two chassis that are foldable and coupled to each other. The first chassis may comprise a coupling recess, and the second chassis may comprise a coupling projection that is received in and coupled to the coupling recess. In the first chassis, the coupling recess may be formed so that a side facing the second chassis is concave in a closed state.
Each chassis may comprise a case member whose depth is substantially equal to a thickness of the chassis. Each case member may comprise an accommodation recess to receive electronic components, and a side of each accommodation recess that faces its counterpart chassis can be concave. In this way, air-tightness (i.e., water-proof property) of the chassis or strength of the chassis can be improved.
However, when the first chassis comprises a case member with a depth substantially equal to the thickness of the chassis, both the coupling recess and the accommodation recess are formed while the facing sides are concave. This requires the accommodation recess and the coupling recess to be in separate regions so as not to overlap each other. As a result, space in the first chassis is not utilized effectively and therefore a size of the first chassis and thus a size of the mobile phone may be larger than they could be if space were used more efficiently.
Therefore, there is a need to establish a balance between a formation of the coupling recess and effective utilization of space in the first chassis.